In a normal human heart, the sinus node, generally located near the junction of the superior vena cava and the right atrium, constitutes the primary natural pacemaker initiating rhythmic electrical excitation of the heart chambers. The cardiac impulse arising from the sinus node is transmitted to the two atrial chambers, causing a depolarization known as a P-wave and the resulting atrial chamber contractions. The excitation pulse is further transmitted to and through the ventricles via the atrioventricular (A-V) node and a ventricular conduction system causing a depolarization known as an R-wave and the resulting ventricular chamber contractions.
Disruption of this natural pacemaking and conduction system as a result of aging or disease may be successfully treated by artificial cardiac pacing using implantable cardiac electrotherapy devices, including pacemakers and implantable defibrillators, which deliver rhythmic electrical pulses or other anti-arrhythmia therapies to the heart at a desired energy and rate. One or more heart chambers may be electrically stimulated depending on the location and severity of the conduction disorder.
Cardiac pacemakers conventionally stimulate a heart chamber by applying current pulses to cardiac tissues via two electrodes, a cathode and an anode. Standard pacing leads are available in either of two configurations, unipolar leads or bipolar leads, depending on the arrangement of the electrodes of a particular lead. A unipolar pacing lead contains a single electrode, normally the cathode, which extends pervenously distal from the pacemaker in an insulating enclosure until it is adjacent to the tip of the lead where the insulation is terminated to provide for electrical contact of the cathode with the heart tissue. The anode provides a return path for the pacing electrical circuit. For a unipolar lead, the anode is the pacemaker case.
A bipolar lead contains two electrodes within an insulating sheath, an anode that extends distal from the pacemaker to a position adjacent to, but spaced from, the electrode tip, and a cathode that also extends distal from the pacemaker, but terminates a short distance distal of the anode, at the lead tip. The anode commonly takes the form of a ring having greater surface area than the cathode tip. An insulating barrier separates the cathode and anode of a bipolar lead. In current pacemakers, circuits for pacing and sensing, which determine tip, ring and case electrode connections, are provided. Thus, the pacemakers may be programmed for either bipolar or unipolar operation with respect to either sensing or pacing operations.
Systems and methods have been developed for determining various operating conditions for implantable cardiac electrotherapy devices. For example, electrode configurations may be determined for sensing and stimulating, cathode and anode assignments may be determined, and coupling intervals may be determined for precisely controlling the activation sequence of electrodes. Determining such operating conditions may be particularly suitable for programmable control systems of implantable cardiac devices.
Although technology for implantable cardiac devices has advanced to provide multiple electrodes that are available for pacing and/or sensing, developing ways to take advantage of such technology is ongoing. It would be beneficial to be able to determine a preferred or optimal pacing configuration for a device implanted in a patient, for example, to provide an efficient electrotherapy and/or to provide an electrotherapy that is less likely to result in arrhythmia.
Thus, there is a need in the art for a system for identifying an electrode or combination of electrodes for a preferred or optimal pacing configuration for a multi-electrode implantable cardiac electrotherapy device. There is also a need in the art for a method of identifying an electrode or combination of electrodes for a preferred or optimal pacing configuration for a multi-electrode implantable cardiac electrotherapy device.